glycoproteins that form part of the cell walls of bacteria (Appendix 3) while the
chondroitins are glycosaminoglycans that occur in cartilage, skin and connect-
ive tissue. Other polysaccharides have specific biological activities. For example,
heparin inhibits the clotting of blood whilst starch and glycogen (Figure 1.21b),
are the main energy stores of mammals, plants and microorganisms. Polysac-
charide residues also form parts of some enzyme and receptor molecules.
OOCH 2 OHHNHCOCH 3HH CH 2 OHHO
ONHHNHCOCH 3HHH
OCOCH 3 HCOOHnTetrapeptide chainPentaglycine cross linkPentaglycine cross linkA lactie
acid
residue
The NAM-NAG glycosidic linkNAMNAMNAGNAGNAGNAGNAMNAMNAGNAMNAGNAMPolysaccharide chains(a)Tetrapeptide
chainsPentaglycine
cross linksO HHHOCH 2 OHetcCH 2 OHOH HHO
HOHOH HHO
HOHOCH 2 OHetc
OOH HHO
HOHO HCH 2 OHOH HHO
HOH(b)CH 2
HCH 2 OH
OOH HCH 2 OHetc OH HHHO
HOHHOH HHO
HOHOOHOCH 2 OHOCH 2 OHOH HHO
HOHetc OH HHO
HOHOH HHO
HOHOCH 2 OH
HOetcOHCH 2 OHOH HHO O
HOHOHHHOH
A fragment of an amylopectin chainA fragment of an amylose chainFigure 1.21 (a) A schematic representation of a fragment of the structure of the glycoprotein (a
murein) forming the cell wall of Gram-positive bacteria. Adapted from G ThomasMedicinal
Chemistry, an Introduction, 2000, John Wiley and Sons, Ltd. (b) A representation of the structure
of glycogen and starch. Both structures are based on chains ofa-glucose residues joined bya-(1,4)
glycosidic links in a similar manner to that found in amylose. In glycogen, these chains are
branched every eight to 10 glucose residues, the branches being attached bya-(1,6) glycosidic
links similar to those found in the amylopectins. Starch consists of unbranched amylose chains
(10–20%) and amylopectins with branches occurring every 20–30 glucose residuesCARBOHYDRATES 19